Magnetic Earth

Earth's magnetic field looks like strands of spaghetti in these two supercomputer simulations from researchers at Los Alamos National Laboratory. The image at left shows the magnetic field in a stable state. The image at right shows it in the middle of a reversal, when magnetic "north" becomes magnetic "south" and vice versa. Such reversals happen on average every few hundred thousand years, with the last about 780,000 years ago. The field grows considerably weaker during a reversal, allowing more space radiation to reach Earth's surface. [Gary A. Glatzmaier/LANL/DOE]

Canada’s about to lose a landmark to Russia. Earth’s north magnetic pole has been in northern Canada since its location was first charted almost two centuries ago. But it’s moving at a rate of close to 40 miles per year. Before long, it’ll be in Russia.

Changes in the magnetic field are nothing new. Its direction and strength vary all the time - on geological timescales, anyway. And sometimes, the field does a complete flip - the north magnetic pole becomes the south pole and vice versa. The last one happened almost 800,000 years ago, and we may be about due for another.

The magnetic field originates deep inside our planet. Earth has an inner core of solid iron that’s as hot as the surface of the Sun. It’s surrounded by a liquid outer core. The two rotate at slightly different speeds. And the outer core is stirred up by heat from the inner core, as well as Earth’s rotation. That creates electric currents, which in turn generate the magnetic field.

The history of the field is preserved in rocks, which are imprinted with the magnetic field as they cool. They show that the field has reversed many times. But they also show that it may take thousands of years to complete a reversal. And there’s no evidence that the magnetic field disappears during these events, it just gets a lot weaker.

A magnetic flip would require some changes - not just from people, but from animals that use the magnetic field to get around. More about that tomorrow.

Script by Damond Benningfield, Copyright 2013

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

[4]

StarDate is brought to you in part through the generous support of our underwriters. Interested in underwriting? Let us know.